1. Field of the Invention
The present invention relates to an energy storage apparatus for railway vehicles by adopting a bidirectional DC-DC converter. More particularly, the energy storage device for railway vehicle is adopting the bidirectional DC-DC converter, which has increased the efficiencies of the charge/discharge. The design of controller is associated the economical operation to increase the efficiency and convenience through the innovation of the function and configuration, so that the capacity of the energy storage is increased.
2. Related Prior Art
The worldwide industrialization has rapidly increased the oil consumption. As a result, our environment has changed. Due to increase the pollutants in our environment, the world's climate has rapidly warmed. To make the matter worse, the natural resources, such as the fossil fuel energy in the world is becoming depleted. Thus, the depletion of the natural resources has caused to raise the oil price steeply. Because the escalation of oil consumption causes to increase the carbon-dioxide in our atmosphere, the Kyoto protocol was established to prevent the global warming. As an urgent project, the research has performed for recycling the energy to reduce the emission of carbon monoxide.
Under such circumstances, the natural energy, such as a wind, tide, solar, or water energy has investigated for utilizing in our life. The new technology has developed to utilize the natural energy for applying in our life. However, the new technology has intensively developed to increase the efficiency. The conventional energy generation device and the storage systems have innovated to improve the certain problems of energy loss for minimizing the loss rate.
In a modern subway, some of trains employ a regeneration brake system to save energy. When the subway train is decelerated, the regeneration brake system converts kinetic energy to the electrical energy and accumulates the converted electric energy. The regeneration brake system is not only reducing the power consumption of the entire system, but also preventing the noise generation by the frictions of brake and wearing of the brake shoes. Regeneration brake system has increasingly applied to the modern train because of such an advantage.
However, the conventional regeneration brake system has a problem of the efficiency of the charging/discharging through the energy storage components. Because the controller of the conventional energy storage apparatus is limited in the function, the conventional controller has merely performed to check the voltage or current, while it is monitoring supercapacitors as the major energy storage components without monitoring the operation of the device.
The regeneration brake system of the conventional energy storage apparatus has a problem of the DC/DC converter and a storage medium. They should be developed for increasing the capacity and efficiency of the energy storage apparatus. For example, when the demand is increased, the capacity of the energy storage apparatus associated with the DC/DC converter and the storage medium from 750V and 10 MJ to 750V and 15 MJ, it is not possible to produce the energy storage apparatus with capacity of 750V and 15 MJ by simply modifying the existing regeneration power storage system with capacity of 750V and 10 MJ. Thus, it is required research to develop and manufacture a new regeneration power storage system having 750V and 15 MJ.
When a 750V, 20 MJ storage medium is needed, a recently developed technology connects a plurality of 750V, 10 MJ storage media to achieve the 750V, 20 MJ storage medium, thereby increasing use efficiency of existing components.
However, an energy storage apparatus which employs such technology needs to include a plurality of units for almost all components (for example, charging units, filter units, current and voltage detectors, and controllers, DC/DC converters, and storage media) and also needs to include an additional current balancing controller to achieve current balancing. Therefore, the energy storage apparatus has problems in that it is necessary to include an additional component such as the current balancing controller without advantages such as a small number of parts and a small volume.